Surat al-A'raf; 95,97,99 (The grounds of devastation of peoples are generally their denying the messengers, their failure to take lessons from and heed afflictions befalling them, their growing arrogant and their cruelty)

Then We gave them good in exchange for evil until they increased in number and said, 'Our forefathers too underwent both hardship and ease'. Then We seized them suddenly when they were not expecting it. (Surat al-Araf, 95)

So they said forefathers had alsosuffered from sucheconomic crisis in the past, this always happens.

Do the people of the cities feel secure against Our violent force coming down on them in the night while they are asleep? (Surat al-Araf, 97)

So in essence Allah says, 'How do they know that I won't send my violent force'.

Do the people of the cities feel secure against Our violent force coming down on them?"

That is, were they secure from Allah's revenge?

No one feels secure against Allah's devising except for those who are lost. (Surat al-Araf, 99)

Meaning Allah says that 'They cannot feel secure', Insha'Allah.The grounds of devastation is generally to deny the messengers, that is to deny Mahdis, not to take lessons from afflictions befalling, not to heed them, to grow arrogant and cruelty. Devastations come about because of these four reasons.